The Decadent Pleasures of Mulch
WASHINGTON – Mulch is practical – it holds moisture and controls weeds. It is also a design element that helps give your landscape a clean, unified look. What mulch should you use on your landscape beds? My first response is always organic material in the form of compost, spread about two inches thick. However, sometimes people really want to know which mulch is most aesthetically pleasing. Then, I recommend two inches of compost with about a one-inch veneer of aged, double-shredded hardwood or pine bark. That way, you get aesthetic appeal as well as the practical benefits of mulch: nutrient production, moisture retention, soil conditioning and weed control. Many materials can serve as mulch, including plastic, newspaper, stone, landscape fabric, wood chips and rubber. I prefer organically based, partially decomposed mulches that condition the earth as they decay, such as compost or the aged, double-shredded bark. Other organic materials that can be used include straw, salt hay, pine needles, ground corn cobs, pine bark nuggets, cocoa bean hulls and licorice root, which is a rare find but an extremely fluffy, dark and handsome mulch.
Rounded river gravel and crushed stone can also be used as ornamental mulch. It’s helpful for covering problem areas, such as soil compacted by heavy foot traffic. Stone mulches can be colorful, and they are available in a range of sizes. I generally don’t recommend mulching planting beds with stone because of the difficulty of getting to the soil. You can’t work compost into soil that has a rock coating, so plants are deprived of the ongoing replenishment of organic material to the soil. Stone is effective as a buffer around the outside edge of trees or as an edging around a bed. With stone mulch, use a porous landscape fabric under it for air and moisture circulation. You will also be able to gather up the stone much more easily when you re-landscape. Volcanic rock, also called lava rock, is a plant-friendly mulch available in numerous colors. It doesn’t allow heat buildup around plants the way regular rock does, and it insulates the soil, keeping it from getting too hot or dry. Trees and shrubs appear to thrive under this material. Wear gloves when spreading volcanic stone because it has many sharp facets. I prefer compost. It adds another element of protection for plants by enriching and aerating the soil. If you are having a problem with a plant, one of the best practices to revive it is to lay a generous amount of compost, two to three inches, over the root system. Another practice for incorporating compost around an installed plant is vertical mulching. Dig holes with a manual posthole digger, or excavate a trench that is 6 inches wide and 8 to 10 inches deep around the outside branch spread (drip line) of a plant. Fill the holes or trench with compost. The deeper you vertically mulch, the better. Make sure decomposition is well underway before applying compost because the microorganisms that cause decay deplete a great deal of nitrogen. If this is a concern, add a nitrogen-rich fertilizer with your green, partially decomposed compost. If you are making your own compost, it’s ready to use when it’s black or dark brown, crumbly and neutral- to musty-smelling. Under the proper conditions – full sun, air circulation and moisture – this can take as little as one to two months, or under less desirable circumstances, six months or more. Depending on how much your compost heats up, it will kill pests. How do you know if you have well-aged mulch? Much of what is sold as bark mulch is not all bark. It contains a lot of light-colored shredded wood that bleaches white in the sun and rain and won’t decay quickly. When you buy mulch, open a bag or go where you can see it piled and look at it. Make sure hardwood bark mulch doesn’t have a high proportion of shredded wood. Look for an even, light-textured dark color. Shredded wood is sharp and fresh-feeling. Lerner is president of Environmental Design in Capitol View Park, Md., and author of “Anyone Can Landscape” (Ball 2001). Contact him through his Web site, http://www.gardenlerner.com.
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